Method and apparatus for detecting metal particles in nonmetallic material



Aprll 1, 1941. w. c. BROEKHUYSEN .237.254

METHOD AND APPARATUS FOR DETECTING METAL PARTICLES IN NONMETALLICMATERIAL Filed Jan. 16, 1937 2 Sheets-Sheet 1 April 1941' w. c.BROEKHUYSEN 2.237.254

METHOD AND TBCTING METAL LIC MATERIAL APPARATUS FOR DE PARTICLES INNONMETAL Filed Jan. 16, 1937 2 Sheets-Sheet 2' INVENTOR WZZ/zzmCBZvahgJv z ATTORNEY Patented Apr. 1, 1941 UNITED STATE METHOD ANDAPPARATUS FOR DETECTING IN NONMETALLIC MA LIETAL PARTICLES TERIALWilliam Broekhuysen, Brooklyn, N. Y., assignor to lnternationalcigar'Machinery Company, a

' corporation of New Jersey Application January 16, 1937, Serial No.120,903

a 12 Claims. (01. 209-81) This invention relates to a method andapparatus for detecting foreign metal particles in nonmetallic materialssuch as foodstufis, tobacco, cigars, etc., in which the presence of suchparticles would be detrimental to their use; and an object is to providea simple and practical device which can be readily incorporated inmachine for packaging or otherwise preparing such materials formarketing;

in carrying out the invention I have illustrated a highly sensitivemethod for detecting the p iesence of metal particles in nonconductingmaterial, in which'the material is passed through the V electromagneticfield of a coil connected in an alternating current impedance bridgecircuit with another identical but oppositely wound coil, both energizedby a third coil insuch a manner that the'two first-named coils arenormally in exact electrical balance with one :another. When metal ispresent. in the material introducedlnto one of the'two identicaldetector coils, thiswill afiect the inductance of this coil and willdisturb the balance, thereby establishing avoltage across the normallyneutral diagonal of the bridge circult. This voltage can be amplified bywellknown means so as to actuate a relay for giving a signal or foroperatinga suitable device for marking or ejecting thedefective'material.

The foregoing" method isespecially advantageous in that nonmagnetic, aswell as magnetic,

metallic particles can be detected.

' The unbalance voltage, after amplification, is rectified (ordetected), and the amplified voltage is coupled to the grid of an outputtube which, in turn, actuates the relay.- According tothe arrangement ofthis coupling, the relay may be caused to operate either when the actualmagnitude of the unbalance voltage across the bridge exceeds a givenminimum value, or when the voltage changes at a rate exceeding apredetermined minimum value. The latter arrangement "is preferable ifthe change of voltage to be detected is fairly rapid as, in that case,the amplifier can be made so as not to react to slow changes caused byvariations in temperature, humidity, etc.

While the detection of foreign metal objects, for obvious reasons, ismost important in foodstufis, in the following description specialreference is had to the application of this device to the detection ofmetallic particles in cigars and to the ejection of such defectivecigars from the cigar machine before they reach the attendant for finalhandling.

Other objects and advantages of my invention will be apparent from theensuing description and claims.

In the accompanying drawings which form a part of this specification:

. g- 1 is a diagram showing the principle of the new metal detector.

Figs. 2 and Sam diagrams showing modifications in the coupling of theamplified voltage to the grid of the output tube.

Fig. 4 is a graph of the electromotive force impressed on the detectorcoils by an oscillator of given frequency, at different tunedfrequencies of the coils.

Fig. 5 is .a sectional side elevation'showing the w mechanicalarrangement of the detector unit consisting of an energizing coil andtwo detector coils.

'Fig. 6 is asectional end elevation on line 6-5 .of Fig. 5.

Fig. 7 is a partial side elevation of a cigar machine showing theapplication of the new metal detector for ejecting defective cigarsbefore inspecting and bunching the finished cigars.

Fig. 8 is an end elevation on line 88 of Fig. 7,

and

Fig. 9 is a plan view of the mechanisms shown in Fig. 7, with a diagramof'their electrical connections. I

Referring to Fig, 1, the current from a vacuum tube oscillator 10,preferably of high frequency, energizes a coil H which induces equal butopposite voltages in two oppositely wound identical coils l2 and I3placed coaxial with coil II at equal distances from its ends. Thecoils I2 and 13 are connected into an inductance bridge circuit by joiningtheir inward ends by wires [4 to one terminal l5 of a high resistance Itand their outward ends by wires l1 throughvariable condensers l8 andI9'to the other terminal 20 of resistor [6. The midpoint l5 of the twodetector coils l2 and I3 is connected by a wire 2! to the input'terminalof a high-frequency amplifier unit 22, while the midpoint 20 of the twocondensers l8 and I9 is connected by a wire 23 to ground, the unit22'being grounded bya wire 24. The oscillator 10 and the amplifier unit22 are sup- I plied with power through wires 25 which may be connectedto any suitable source of alternating or direct current. The oscillatoris connected to the unit 22 by a cable 26 which contains the necessarywires leading to its various elements.

By means of the condensers I8 and IS, the coils l2 and I3 can be tunedto any frequency with respect to the oscillator frequency. If the twosides of the bridge circuit are thus tuned to. the same frequency andare perfectly symmetri-- cal otherwise, the bridge circuit is in perfectelectrical balance and the voltage betweenpoints I5 and 20 will be zero.Any change in the inductance of one of the coils l2 and 13 such as maybe caused by .the presence of a piece of metal in an article ,A whenpassed through the field of one of them, will disturb this electricalbalance and a high-frequency voltage will be developed between points I!and 22 and will be impressed by the wire 2| on the amplifier unit 22.Resistance It serves merely for preventing anaccumulation of charges oncondensers I2 and paralyze the first tube of the amplifier unit 22.

distances above and. below .the oscillator frequency Po, the impressedvoltage being the same in both. In practice,'these points E1 and E2 are.The amplifiedhigh-frequency voltage delivered l .byunit'22 is impressedthrough the inductively ,fcoupled coils 21 and 28 on the rectifier plateI.

of the detector output tube ll.

voltage is impressed. across a condenser 48 and fa 'high-resistancelll,and may be either pacitively-coupled tothe Erid 22 of the output tube llthrough acoupling condenser-2| anda gridleak It. asshown in Fig. 1. orit may be directly inipressed on-the grid, as shown in Fig. 2.

If the coupling is capacitive, asshown in Fig.

.'1,' only aI-chang'e'in'the rectified voltage will be 1 I impressed onthe grid of the output tube, pro-1- 'vided therat'e of change exceeds acertain minimuni value depending onthe relative magnitudes of thecoupling-condenser l2 and the Brld-leak resistor 39. If thehighefrequency'voltage across The found to be at approximatelyone-halfoi the peak voltage Ee obtained at exact resonance with the fixedoscillator. The coils "and it must be' tuned to the samefrequency and.not-tothe same resulting impressed voltageat opposite sides fcapa'cities of condensers ll and-J2, but in direct opposition, "or exactlylaoelect'rical degreesjout of; phase. he anti adjustment to this end maybe obtained by 'l lfflni the energizing, coil ll slightly to one side orthe other as'rej-j quired.- 1 r 1 'jFo'r. p p rjdllibtlheht and adequateshieldv I ofthe oscillator frequencyl'b, because,- in ordernecessary-that the1 -,voltages= across the It to obtainjzizero" voltage'resistor inn is and It. are'uot iflyinverselyto the ing,'the'threecoi ls|,2."anu l2 are'in practice assembled .in-unit.,.In Figs; 5 and .6, thearrangement of ifide'tector 'init'for comresistor I8, and'consequentlyalso the rectified voltage across condenser, increases faster-than 'thisrate, a negative potential will be impressed I f on grid 28, and thecurrent from plate 3| to cathode 42 of tube II, which flows also throughrelay coil 32 and wire 22, will be reduced to such.

an extent that the relay armature is-released and contact it closes. Theplate current supply is obtained from. the positive side of the platesupply in amplifier 22, the negative side of which is grounded. Theclosing of contact 34 allows current to flow from the line 2! by wires35 a through the operating coil of an electromagnetic device 31, whichejects the article A on its emergence from the detector unit, if foundto contain metal. with this arrangement the relay will not react toslow-voltage changes across resistor l6 caused by variation oftemperature, humidity, etc.

papatively objects.- such}! l aves -01 bread, candy bars, etc. ,-is Thecoils ll, l2, and. I2 are'wound on the'center section 42 and- .the endsections llout from a tube-oilinsuiating materiahthe end sections llbeing fastened in annular metallic'end disks Ii held together by'agrounded .metal cylinder II'. shi'elding the coils againstlexternalinterference. The

- center section 4,! issupport'ed by an annular disk I of insulatingmaterial, thisdisk being fastened by cleats I to theshieldcan l2 andhavn the rectified voltage is directly impressed.

by wire 40 on the grid 2! of the output tube 20,

as shown in Fig. 2, the relay 22 will drop out whenever the voltageacross resistor It exceeds a given minimum value governed by the degreeof amplification obtained by the unit 22 and by the characteristics ofthe output tube II. In Figures 1 and 2, the two functions of rectifierand output tube are combined in one tube 20 of the duo-diode-triodetype.

As a third possibility, the amplified high-frequency voltage may bedirectly impressed through wire 40 on the grid 29 ofa grid-controlledrectifier tube 43 of the thyratron type, as shown in Fig. 3, a battery44 being inserted between coil 28 and ground wire II to produce anegative bias on grid 29. In the latter arrangement, the relay 32 willpull in whenever the bridge voltage exceeds a certain minimum value, andwill be held in, even after this voltage has disappeared, until aninterrupter contact 42 in series with the relay coil 32 is momentarilyopened.

For best results, the coils l2 and I 2 should be tuned to resonance at afrequency somewhat above or below the frequency of the oscillator llat apoint near the peak of the frequency-voltage curve of the detector coilswhere the steepness oi the curve is greatest and therefore a givenchange in resonant frequency will cause a maxi- 'ing an extension llprotruding through an opening in can H. The extendingarm II is supportedon' along screw it held in fixed position on the formerby collars l1pinned on the latter. .The

screw. It is threaded into engagement with one of theend disks llsothat, by turning the same,

the position of coilll relative to the coils l2 and I2 can be adjustedfor exact electrical balance. In order to prevent any change in theelectrical balance which might be. caused by the nonmetallic objectitself when passing through the coils,

l-T Z shielded electrostatically. For this purpose, an insulating tubeIt is mounted inside of the tubes 42 and ",thetube 88 carrying a layeroi fine copper wires ll spaced at equal intervals parallel toitsaxis'and connected at one orboth ends to a metal ring ll inserted into acounterbore of disk II and in electrical contact therewith. In order toprevent the adjustment of the inductive balance of the coils ll, l2, andII from aifecting their electrostatic balance, the coil ii iselectrostatically shielded from coils l2 and II by grounded open radialwires II attached to one or both sides of annular disks '2 mounted inthe spaces between tube sections ll and- I by means of the cleats 54 andof brackets 23 which latter also serve as guides for the screw ll.

Coils l2 and It are at equal distance on opposite sides of coil II andare identical in number of turns and sizes of wire, but woundin oppositedirections. They are tuned to the same frequency and have equalimpressed voltages which balance each other. A variation in oscillatorfrequency will affect both coils to the same degree and therefore willnot disturb the balance of the bridge. But a particle of metal enteringthe field of either one of these coils will cause an unbalance of thevoltage which may be made to eject the article containing the metalafter 11:21:: the detector unit, as will be described hereter.

Coils l2 and I3 do not have to be mounted in the same shield can 52, butmay be mounted in Separate shields and the object to be examined passedthrough only one of them. They may be coupled to the oscillator eitherinductively as shown in Fig. l, or capacitively through condensers inthe well-known manner. The greatest stability is obtained, however, witha perfectly symmetrical arrangement, as shown in Figures 5 and 6. Forexamination of foodstuffs, such as flour, cereals, etc. in bulk, theunit shown in Figures 5 and 6 may preferably be mounted vertically or atan angle, and the bulk-material passed through tube 58 by gravity.

The application of my invention to thedetection of metal in cigars andto the ejection of the defective cigars from a cigar machine is shown inFigures '1, 8, and 9. While the invention may be applied to thedetection of metal in the tobacco 'of the cigar units at any of thevarious stages in the formation of the cigars by the cigar machine, as,for example, prior to the application of the wrappers, I haveillustrated it as applied to the cigar units after leaving the reroller64. In a cigar machine, the finished cigars are delivered from thereroller," in which-they are smoothed out, knurled and trimmed to size,to an inspection table 65 from which the operator takes them for handknurling and other finishing touches and for final stacking into thebundletray. In order to prevent metal-containing cigars from being thusdelivered, the inspection table 65 is shown provided with an endlessbelt 66 which carries the cigars C through the abovedescribed metaldetector to an electromagnetic deflecting device 51 which, controlled bythe detector, causes the perfect cigars C to fall onto the table whilepermitting faulty cigars C" to pass beyond the same.

From the reroller 64, the cigars C are deposited on belt 66 by a guide68. The belt 66 runs from a pulley 69 on a shaft 1 0 to a pulley H on ashaft 12 driven through a pulley 13 by a belt 14 from a pulley 15 on adrive shaft 16 of the cigar machine. The shafts l0 and 12 are carried byside plates Tl attached to blocks 18 fastened to table 65, the belt 66being sup rted by plates I9 and 39 carried by blocks 18. The supportingplate 80 at the delivery end of belt 86 has a transverse inclinedextension 8! on which the cigars 0', free from metal particles, rollonto table 65.

The cigar, upon emerging from the unit 82 which contains themetal-detector coils H, l2, and 83, the oscillator l 0, amplifier 22,rectifier and output tube 30, relay 32 and contact 34, encounters thedeflector 51 which by a block 83 is aflixed to a vertical shaft 84supported by a bearing 85 attachedto side bar TI. On shaft 84 is mountedthe armature 86 of an electromagnetfllwhich is energized by the coil 36controlled by the contact 34 of the detector relay 32. The electromagnet81 is fastened between the loops of belt 66 to block 18. The armature 8Bis held by a spring 38, anchored on a post 89 in side plate ll, in theposition shown in full lines in Fig. 9, in which position the deflectorplate 61 is in an oblique position across the belt 66. In this position,the cigar C is guided onto the incline 8| and rolls upon table 55. Whenmetal is detected in the cigar, the contact 34 is closed by the relay32, thereby the coil 36 is energized and the armature 8B is attractedinto position 86', shown in dotted lines, by the electromagnet 81, thuscausing the shaft 84 to turn the deflector 6'! into the parallel longerdeflected but is carried by the belt 66 beyond the edge of table 65.

electromagnet 81 energized until the circuit is position 61' in whichthe faulty cigar C" is no automatically broken in each cycle of themachine by a release contact 48 held in closed position by a roller 92riding on the circumference of a cam 93 on shaft 16, this cam having adepression 94 so positioned as to properly time the momentary opening ofcontact 90.

When the relay contact 34 closes, in the event of a faulty cigar,current from the line 25 and wire 35 passes through wires 95 and 96,which are joined at one side of contact 90, to one terminal of thenormally closed release contact 48 and from its otherterminal throughwire 91 to the electromagnet-coil 36, returning through wire 98 to theline 25. This momentary current, through the attraction of armature 86,causes the pin 9| to close contact 99 so that, upon opening of contact34, the current from line 25 then passes from wire 35 through wire 99 tocontact from which it reaches the coil 36 through wires 96, 9! andcontact 48, returning from coil 36 to the line by wire 98 as before.This circuit through contact 99 remains closed until the contact 48 isopened by cam 93, whereupon the armature 86 returns to its normalposition and the contact 90 reopens, thus replacing the entire detectorsystem into starting position, ready for the next cigar arriving on theforwarding belt.

It will of course be understood that when the magnet 36 is energizedfrom the thyratron tube illustrated in Figure 3, the holding circuitabove described is unnecessary, since the relay 32 remains energized andmaintains the circuit through magnet 36 closed. In this case, thecontacts 48 are positioned in series with the relay coil 32, as will beapparent. a

The terms and expressions which I have employed are used as terms ofdescription and not of limitation, and I have no intention, in the useof such terms and expressions, of excluding any equivalents of thefeatures shown and described or portions thereof, but recognize thatvarious modifications are possible within the scope of the inventionclaimed.

I claim:

1. Apparatus for the detection of metallic matter in nonmetallicobjects; said apparatus comprising a coil having an air core, means forenergizing said coil, means for conveying a series of said objectssuccessively through said coil, and

3. Apparatus for the detection of metallic mat ter in nonmetallicobjects, said apparatus comprising a pair of axially-spacedoppositely-wound coils, insulating means supporting said vcoils, a

third coil interposed between the coils of said pair, insulating meanssupporting said third coil, shielding means surrounding said coils forprotecting the same against external interference, means for adjustingsaid third coil axially with respect to the gthers of said coils, a tubeof insulating material within said coils and provid ing a passage forthe travel of objects therethrough, a plurality of wires surroundingsaid tube and shielding said coils electrostatically from said objects,a pluralityof insulating members interposed between said third coil andthe others of said coils, each of said insulating members carryingradially extendin wires for shielding said other coils electrostaticallyfrom said third coil.

4. Apparatus for the detection of metallic matter in nonmetallicobjects, said'apparatus comprising a pair of end metallic disks, a metalshell connecting said disks, tubular members of insulating materialmounted in said disks, coils carried by said tubular members, a thirdtubular member, interposed between the first mentioned tubular members,a coil mounted on said third tubular member for inducing electrcmotiveforces in the first mentioned coils, a disk of insulating materialmounted in said shell and supporting said third tubular member, the lastmentioned disk having an arm extending through an opening in said shell,means engaging'said arm for shifting said disk and said third tubularmember to arh'ust the coil carried thereby along the axis of the firstmentioned coils, an insulating tube mounted within the first mentionedtubular members and providing a passage for the travel of objectsthrough said coils, wires carried by the last mentioned tube andconnected electrically with said and disks for shielding said coilselectrostatically from said objects, disks of insulating materialpositioned between the aforesaid third tubular member and the firstmentioned tubular members, and radially extending wires mounted on thelast mentioned disks for shielding the first mentioned coilselectrostatically from the third coil. i

5. In combination with a cigar machine including means for conveyingcigar units along a given path, means responsive to the presence oi.metal in a cigar unit, means for shielding said metal-responsive meansfrom the electrostatic disturbance by said cigar units, means forshielding said metal-responsive means against disturbances from saidcigar machine, and means controlled by said metal-responsive means fordesignating a unit in which metal is present.

6. In combination with a cigar machine including means for conveyingcigar units along a given path, means responsive to the presence ofmetal ina cigar unit, means for shielding said metal-responsive meansfrom the electrostatic disturbances by said cigar units, means forshielding said metal-responsive means against disturbances from saidcigar machine, and means controlled by said metal-responsive means forcausing a unit in which metal is present to be ejected from the machine.

7. The method of detecting the presence of particles of metal embeddedin nonmetallic ma terial many times greater in bulk than said parbetweensaid material and an impedance bridge to cause metal present in saidmaterial to de- -ticles which comprises setting up relative motion velopa voltage between certain points on said bridge, shielding said bridgeagainst electrostatic disturbances from said nonmetallic material, andapplying said voltage to the production of an eilect indicative of theportion oi said material in which said metal is present.

'8. Apparatus for. the detection of metallic matter in nonmetallicobjects, said apparatus comprising a coil having an air core, means forenergizing said coil, means for conveying a series of objectssuccessively through a region influenced by said coil, and means betweensaid coil and the path of travel of said objects for shielding said coilagainst electrostatic interference from said objects.

9. Apparatus for the detection of metallic matter in nonmetallicobjects, said apparatus comprising a pair of axially spaced coils, athird coil connected to a source of electrical energy and arrangedintermediate the first-mentioned coils for energizing the latter, all ofsaid coils having air cores, means for conveying a series of objectssuccessively through said coils, and means between said coils and thepath of travel of said objects for shielding said coils againstelectrostatic disturbances from the passage of said objects through saidcoils.

10. The method of detecting the presence of particles of, metallicmatter embedded in nonmetallic objects many times greater in size thansaid particles, said method comprising applying a high frequency voltageto a balanced impedance bridge, passing said objects successivelythrough an electro-magnetic field produced by said bridge to therebycause metallic matter in any of said objects'to disturb the balance ofsaid bridge, and to develop a voltage between given points, shieldingsaid bridge against electrostatic disturbances by said objects duringthe travel of the latter through said field and applying said voltage tothe production of an eflfect indicative of the object in which metallicmatter is present.

11. Apparatus for the detection of metallic material in nonmetallicobjects, said apparatus comprising a source of alternating current, animpedance bridge containing a coil having an air core and energized bysaid source, means for passing a series of said objects along a givenpath through an electro-magnetic region produced by said coil to therebycause metallic material in any 01' said objects to change the inductanceof said coil and to disturb the balance of said bridge to therebydevelop a voltage between certain portions of said bridge, means betweenthe path of.

travel of said objects and said coil for shielding said coil againstelectrostatic disturbances from said objects, and means rasponsive tosaid voltage for designating any object containing metallic material. i

12. Apparatus for detecting metallic matter in nonmetallic material,saidapparatus comprising a coil having an air core, means for energizingsaid coil, means for passing nonmetallic material into a magneticfield'linked with said coil, means responsive to the effect of metallicmatter upon said field for designating the portion of said materialcontaining said matter, and means between the path of travel of saidmaterial and said coil' for shielding said coil against electrostaticinterference from said material.

WILLIAM C. BROEKHUYSEN.

